During the last thirty years, numerous so-called second generation phototypesetters have been marketed. These machines flash-illuminate characters positioned upon a whirling character disk or drum, and the resulting optical image is projected by a lens system upon a photosensitive film. The size of the characters is changed by means of moving zoom lenses or the like, or by rotating a lens turret to position various lenses at the optical projection axis. The characters are sequentially recorded upon the photosensitive film by mechanically scanning such film which may be accomplished in various ways. The film carriage may be moved relative to the optical axis, the projection lenses may be moved relative to the film platen, the whirling character disk may be moved relative to the film platen, or various combinations of the foregoing may be employed to sequentially project the characters upon the film to form a line of characters. Generally, the projection lens carriage assemblies are relatively heavy and bulky, as is the drum or disk bearing the images of the characters to be projected. Also, changes in the fonts involve manual replacement of the character disk, or film strips mounted upon a drum. Additionally, the electromechanical stepping devices for producing the above-mentioned scanning motions are also relatively bulky and cumbersome. The speed of these second generation machines is limited by the output carriage escapement speed and by character access time determined by the rotational speed of the font disk.
Third generation phototypesetters were introduced in the 1960's to overcome the deficiencies of the second generation phototypesetters. Most of these new typesetters utilize cathode ray tubes for generating the characters upon the face of the tube. These character images are thereafter optically projected upon the film. In contrast with the components of the second generation machines, the electron beam is inertialess and higher character-producing speeds could be generated. Various font families may be generated by these machines since the character-generating codes may be densely packed during recordation upon a magnetic storage media, such as floppy disks. Additionally, the character size may be electronically changed by changing the length of the beam faces comprising the character components. However, while these third generation machines are faster, more accurate and more flexible than the second generation machines, the cost of these new machines is much greater than the second generation machines.
U.S. Pat. Nos. 3,952,311 issued to Lapeyre; 4,090,206 issued to Pfeifer et al; 4,096,486 issued to Pfeifer et al; 4,107,687 issued to Pfeifer et al; 4,318,597 issued to Kotani et al and 4,376,282 issued to Kotani et al as well as Swiss Patent No. 568,593 were developed as improvements to the third generation phototypesetters. All of these references utilized a light-emitting diode (LED) array to produce images which are recorded on radiation-sensitive recording material. With the exception of the Pfeifer et al '206 patent, all of the LED arrays are immobile and span virtually the entire width of the recording material. Images are recorded onto the material by continuously or intermittently advancing the radiation-sensitive material perpendicularly through the radiation generated by the LED array. Pfeifer et al '206 illustrates a method and apparatus for recording images onto a radiation-sensitive medium by utilizing an LED array which is not completely immobile. However, this array merely oscillates as the radiation-sensitive paper passes thereunder to provide a better resolution.
U.S. Pat. No. 4,342,504 issued to Ebner is an improvement upon the immobile printing head described in the above-noted patents and utilizes a printing head which traverses the width of the radiation-sensitive material. This printing head is connected to an LED matrix via a plurality of fiber-optic ribbons. The matrix in turn is connected to circuitry for producing the proper response from the matrix at a particular point in time. The movable printer head is connected to a carriage mechanism to allow the printer head to traverse the radiation-sensitive material at a particular speed in relation to the data supplied to the matrix and in turn the radiation pulses supplied to the printing head. However, while Ebner '504 describes a phototypesetting machine which is relatively inexpensive and accurate, problems have arisen in the construction and utilization of this device. Although this phototypesetter is constructed only with the use of robotics, the attachment of each and every optic fiber between the LED matrix and the printhead is laborious, time-consuming and relatively inaccurate due to the fine tolerances which must be maintained. Additionally, the use of robotics itself is a relatively expensive proposition and the number of units produced is limited to the number of robots available. Furthermore, each fiber band is fragile and susceptible to breakage, and the resolution of the light produced at the head is fixed and limited by the fiber diameter.
U.S. Pat No. 4,378,149 to Ebner has been developed to overcome some of the problems enumerated with respect to the Ebner '504 patent. This patent describes a high-speed character printer in which the LED matrix is directly provided on the face of the movable printhead, thus eliminating the fiber-optic bundle. A cable is provided between the printhead and a signal source to indicate which of the LED's are to be activated at a particular time. As was true with Ebner '504, the printhead traverses the width of the radiation-sensitive material when the material is stationary, and after the head has traversed to the edge of the radiation-sensitive material, this material will be advanced. However, while Ebner '149 is an improvement upon Ebner '504, both of these phototypesetters suffer from the disadvantage of employing a printhead which must contact the radiation-sensitive material. The printhead utilized in both Ebner patents has a metal/glass interface with the sensitive emulsion which typically can scratch the emulsion. Additionally, both of these patents utilize solid-state integrated circuits for driving the LED's provided on a substrate not directly in proximity with the printhead.